1. Field of the Invention
The present invention relates to the art of explosively breaking or cutting solid materials, and has particular, although not exclusive, application for the breaking or cutting of metals for the separation of components of an integral structure.
2. Description of the Prior Art
Explosives are used as convenient sources of energy which can be suddenly released to perform work on solid materials. Uncontrolled fracturing of solids by means of explosives has been accomplished by various methods such as shattering by brute force using a large amount of explosive. Thus, a simple known explosive charge is the "plaster charge" which consists of a mass of high explosive in a compact or linear configuration and which is placed in intimate contact with the surface of a solid body of material, for example, a metal plate, upon which work is to be performed. When the charge is detonated, a shock wave travels through the plate. Provided a medium, such as air, of lower density than the metal plate is in contact with the opposite side of the plate, the shock wave is reflected back from the interface between the plate and such medium. In the process the shock wave undergoes a phase inversion so that a compression wave travelling towards the interface is reflected back as a tension or stretching wave. The actual pressure within the plate at a given point is a summation of the compression and the tension waves.
Plaster charges tend to cause a flake of metal to be torn from the plate on the side thereof opposite to that against which the charge was placed. If sufficient explosive is used, the metal plate may be weakened to such an extent that residual explosive pressure blows a hole through or severs the plate. The use of plaster charges, although simple, requires large amounts of explosive, produces very ragged cuts, causes distortion of the metal adjacent the cut and may result in the projection of destructive fragments of metal.
Various proposals, as disclosed in the following U.S. Patents have been made in the prior art for imparting directionality to the energy release occurring upon the detonation of explosives to perforate, distort, fracture, cut or otherwise modify the shape of solid metal of other hard materials: U.S. Pat. Nos. 1,531,555 granted Mar. 31, 1925 to J. W. Harris, et al; 2,758,543 granted Aug. 14, 1956 to C. W. Grandin; 3,076,408 granted Feb. 5, 1963 to T. C. Poulter, et al; 3,971,290 granted July 17, 1976 to J. W. Blain; 3,373,686 granted Mar. 19, 1968 to J. W. Blain, et al; 4,408,535 granted Oct. 11, 15 1983 to S. C. Alford; 3,486,410 granted Dec. 30, 1969 to V. W. Drexelius, et al.
Thus, a method of more precisely cutting a body of solid metal is by means of shaped charges such as linear cutting charges. A linear cutting charge, in a preferred form, comprises a length of metal which is semi-circular or V-shaped in cross section and an explosive which extends the length of the metal and which is capable of sustaining detonation with a high velocity of propagation. The length of metal is arranged with the hollow side thereof directed towards and spaced away from the solid body on which work is to be performed while the explosive extends centrally of and in contact with the opposite side of the length of metal. With a semicircular section length of metal, the explosive, when detonated, acts to turn the length of metal inside out and project it as a high velocity metal jet at the solid body upon which work is to be performed, the latter thus being severed if the explosive charge is sufficiently powerful. In the case of a V-section length of metal, the pressure exerted by the explosive when detonated, serves to drive the two limbs of the V-section length of metal towards one another at high velocity so that they collide. As a result of the collision of the two limbs, a small part of each of the limbs is stripped off and is projected at the solid metal body on which work is being performed as an extremely fast-moving blade-like jet which is capable of producing a very deep and narrow cut in the solid metal body for a given amount of explosive.
Shaped charges generally produce deeper cuts with less explosive and cause less damage to the solid body on which work is being performed than plastic charges. Shaped charges suffer from disadvantages, however. If the explosive charge is not matched to the metal and thickness of the solid body upon which work is to be performed so as to just cut through the solid body, then the extremely fast moving metal jets produced by the shaped charges can cause considerable damage beyond the solid body upon which work is being performed. Another disadvantage is that the shaped charge has to be spaced from the solid body by a distance of about one or two charge widths, sufficient to allow the aforesaid high velocity jets to develop. A further disadvantage with shaped charges is that those used for producing deep cuts of a centimeter or more are invariably rigid and cannot be bent to follow the contour of a solid body having a curved surface or to produce a cut other than that for which the charge was designed, that is, a non-rectilinear cut in the case of a rectilinear charge.
Linear shaped charges fully encased in a metal sheath are also known. Such charges, however, produce high velocity destructive fragments which are propelled away from the direction of the desired cut. In order to preclude damage from such fragments, relatively heavy protective structures are required to shield and protect personnel as well as sensitive material and components. Pressure fracturing requires relatively heavy backup structures to contain the explosive backblast and to maintain sufficient pressure to obtain the desired fracturing effect with a minimum amount of explosive. In any system where weight is a consideration, this is a serious disadvantage.
Thus, there is a need and a demand for an improved lightweight linear explosive system for the breaking and cutting of metals for the separation of components of an integral structure, whether flat or curved, and which is operative to impart directionality to the energy release thereby to provide a single fracture line with little or no resulting fragments or other debris.